'For I delivered to you first of all that which also I received: that Christ died for our sins according to the scriptures; and that he was buried; and that he has been raised on the third day according to the scriptures.'
'First of all.' This had been his first concern when he came to them, for it was why he was sent by the One from Whom he received it.
And what is the Gospel which he delivered to them? It is the Gospel that he 'received', both directly by revelation from God (Galatians 1:16-17), and also from the Apostles whom he later consulted (Galatians 1:18; Galatians 2:2). Just as he stated that the prophets should be 'judged' so did he submit to the judgment of others the revelation that he had received, as we must also when we receive special insights.
'Received' and 'delivered' were technical terms among the Jews referring to the passing on of authoritative tradition. Thus Paul makes quite clear that the Gospel he preaches is a Gospel that was preached before he arrived on the scene, and is the same Gospel as was preached by the Apostles, and was long prophesied in Scripture. And that Gospel is that 'Christ' died for our sins, in accordance with the Scriptures, was buried, and that he has been raised on the third day according to the Scriptures (compare Luke 24:45-47).
'Christ died for our sins.' Note the title. It was 'the Christ' Who died for our sins. It was the Christ Who suffered. It was the Lord Jesus Christ in the totality of what He was as God's anointed Who died. It was God's chosen and anointed One Who suffered. And that was just what the Scriptures had taught in, for example, Isaiah 52:13 to Isaiah 53:12, backed by all the Scriptures which pointed to deliverance through suffering, whether of man or sacrifice (e.g. Psalms 22; Daniel 9:26; Zechariah 13:7 with 1 Corinthians 9:9 and 1 Corinthians 13:1). So the real death of the Christ is declared. His body was a part of what He was.
'For our sins.' Contrast 1 Corinthians 15:17 and compare Galatians 1:4; Romans 4:7; Ephesians 2:1; Colossians 1:14; Titus 2:14 and see Isaiah 53:4-6; Isaiah 53:8; Isaiah 53:11-12 LXX). Christ is here declared to be an atoning sacrifice (compare 1 Corinthians 5:7) dying for men's sins, and bearing in Himself the sins of all who call on Him (compare 2 Corinthians 5:21). In the words of Jesus, with the Servant of Isaiah 53 in mind, He gave His life 'a ransom in the place of many' (Mark 10:45).
That Jesus was early identified with the suffering Servant of Isaiah comes out in that He was declared to be the Servant at His baptism - 'my beloved, in whom I am well pleased' (Mark 1:11 compare Isaiah 42:1) and the idea is applied to Him in Matthew 12:17-21; Luke 2:32; Luke 9:35 (RV/RSV); Luke 23:35, and we might add John's declaration that He was the Lamb of God Who had come to take away the sins of the world (John 1:29). For the fact that He identified Himself with the Servant see Mark 10:45; Luke 22:37, and He also identified Himself with the anointed one of Isaiah 61:1 (see Luke 4:17-21).
'He was buried.' The certainty of His genuine death comes out in that He was buried. This was no illusion, no pretence. In His physical body He was assuredly laid in the grave. He was dead, stone dead. This was testified to by those who had been there. This stated fact demands that the next clause refers specifically to physical resurrection from that grave, and therefore to the reality of the empty tomb.
The importance of this in Paul's argument is that the fact that He was entombed, and that Jesus was then seen to have been raised from that tomb, demonstrates that His resurrection was a genuine bodily resurrection.
'And that he has been raised on the third day according to the Scriptures.' And in that body, lying as it was in the grave, He was raised again from the dead, and this too was in accordance with the Scriptures. (See especially Isaiah 53:10-12 with Isaiah 25:8; Isaiah 26:19; Hosea 6:2). Note the perfect tense, He rose and still lives. The resurrection of the body was important because it stressed God's complete deliverance. The curse of sin had been wholly removed. His resurrection was the beginning, and in its significance the source, of the redemption of the whole creation (Romans 8:20-21).
'On the third day.' The Gospels tell us that Jesus Himself forecast that He would die and rise again after three days, or on the third day (Matthew 16:21; Mark 8:31; Mark 9:31; Mark 10:34; Luke 9:22), and that was in fact the period after which the resurrection took place. Indeed given the significance of 'three days' as regularly indicating 'a short, complete period' any other period could hardly have been used to mean 'almost immediately, within a short period'; for 'three days' is shorthand for any complete period from one and a half to around five days (compare its use in Joshua 1:11; Joshua 2:16; Joshua 2:22; Joshua 3:2). In Jewish literature even so definite a period as 'three days and three nights' could indicate a part of a day, a day and a part of a day. (We can also compare how in Genesis any shortish journey is a 'three day' journey, and a longer one a 'seven day' journey).
'According to the Scriptures' may not apply to the length of time, but if it did so the thought in mind is probably Hosea 6:2 where the period from Israel being smitten to its rising up is three days also, that is, it will take place 'in a short fixed time period determined by God' (compare 2 Kings 20:5; Jonah 1:17). Later Jewish literature for this reason saw three days as signifying a period resulting in divine deliverance. Jesus may thus have been seeing Himself as accomplishing what was prophesied to happen to the nation. As the suffering Servant He represented Israel. Compare also how He said, 'Destroy this temple and in three days I will raise it again', that is 'within a short, divinely determined period of time' (John 2:19-22).
If the Jewish belief that the body began to corrupt three days after death was held at this time then the promise that 'nor will you give your Holy One to see corruption' (Psalms 16:10), utilised by Peter in Acts 2:15, could also be seen as prophesying a resurrection within three days.